Many combustion devices, such as stoves, fireplaces, and internal combustion systems burn fuels that generate unburned particulate matter which is carried by hot exhaust gases through an exhaust duct into the atmosphere. A portion of the unburned particulates normally condense on the lining of the exhaust duct to form a coating of the unburned particulates. The accumulation of unburned particulates on the exhaust duct is particularly acute in a so called air tight combustion system in which the oxygen available to facilitate combustion is minimized. In the case of stoves or fireplaces which burn solid fuels, this accumulation of unburned particulates is in the form of a creosote coating.
A substantial accumulation of unburned particulates on an exhaust duct presents a definite fire hazard, as those skilled in the art have long recognized. In order to avoid such fire hazard, it has been necessary in the past to either manually "sweep" the unburned particulates from the exhaust duct on a relatively regular basis, or burn the accumulated particulates by generating a particularly hot fire in the combustion chamber. Both of these approaches are effective for removing the unburned particulates; however, it has been heretofore impossible to determine specifically when the unburned particulates have accumulated on the exhaust duct to a dangerous level. Thus, in order to assure that a fire hazard was avoided exhaust ducts were cleaned more often then necessary, thereby resulting in wasted effort and energy resources. In some cases, particulates are no doubt allowed to accumulate beyond a hazardous level, thus posing a risk of loss of life or property.
It is therefore a primary object of the present invention to overcome each of the deficiencies mentioned above and to provide a method and apparatus for monitoring the accumulation of unburned particulates on the exhaust duct associated with a combustion system.
Another object of the invention is to provide a monitoring system of the type mentioned above which provides a visual or audible warning when the particulates have accumulated to a potentially hazardous level.
A still further object of the invention is to provide a monitoring system as described above which is capable of monitoring dissipation of accumulated unburned particulates which are burned by a particularly hot fire in the associated combustion apparatus.
These and further objects of the invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the invention.